Hey guys,


One again i hate posting about questions on my truck but you guys are the best!any help on this would be much appreciated!This is for a 1978 C-10 Shortbed

Here is my combo
.030 over 350
Holley 750 DP
Rpm Air gap
Performer rpm aluminum heads
10:1 compression
Voodoo .489/.504 cam #60103
TCI Streetfighter 3000 stall
3:42 gear ratio factory limited slip 10 bolt
street tire size is 255/70/15

Im thinkin i need a lil lower gear for the track, I run 1/8 plus the occasional stock gt stoplight to stoplight
Best run at track was
9.1 @ 76mph 2.1 60ft on street tires

I have 275/60/15 et street radials ran them and it wouldn't lock both tires and ran a best of 9.2. I kno for sure i need to get a better unit in the rear have been lookin at Eaton unit and it looks like most of you guys on here like there diff.But i am debating on either 4:10's or 3:73's my goal is to get that 60ft down. I drive this truck no more that 55mph city driving and am not worried about mileage.I will be puttin the factory 12 bolt back in also.I want the 4:10's but wanna here what you guys have to say!


Thanks in advance
Byron

going from 3.42's to 3.73's you may not notice enough of a difference. Go for the 4.10's.

Dave

Or a 3.90 ratio.

Do you kno if they make a 3.90 truck 12 bolt gears? I got the 10 bolt in the truck right now i got it from the junkyard to swap out the 12 that the truck had in it but if i do all this rear end stuff i wanna go back to the 12 and sell that 10.

How much do you guys think my 60 ft will go down the 4.10 swap?

i'd say to get the 4.10 gears, and if you do decide to make it into an interstate cruiser, throw an overdrive trans in it.

Do you kno if they make a 3.90 truck 12 bolt gears? I got the 10 bolt in the truck right now i got it from the junkyard to swap out the 12 that the truck had in it but if i do all this rear end stuff i wanna go back to the 12 and sell that 10.

How much do you guys think my 60 ft will go down the 4.10 swap?

FYI the truck 10 bolt is stronger than 12 bolt truck many people feel. The truck 12 bolt is not same as passenger 12 bolt it has smaller than 10bolt pinion gear check it out.

Yea i have heard that from a few people,The 10 bolt that is in the truck came out of a 1987 truck from what i have read it is a 28 spline and from 89 and up the went to the 30 spline,i haven't seen and ring and pinion sets for the 28 spline thats kinda why i am leaning towards goin back to the 12

the ring and pinion gears are the same regardless of how many splines are on the axles.
the same gears will fit any car from a 72 Nova to a 96 Impala SS, and most trucks from the late 70's to the current model.

i have a 77 longbed, i run a 16.2 in the 1/4 with 4:10's on a 28 in. tall tire and i wish i had more gear,i'd go with 4:10's at the minimum

If you're not worried about milage and want more zip, go for the 4.10s. You're running a tall tire so you need more gear. I'm running 4.10s in my 2007 K2500HD and with the 285/70-16s it make a nice combo. Just make sure you get the right gears, just 'cause it's got 12 bolts on the cover doesn't mean it's the same as a car 12 bolt!

Thanks for clearing that up novaderrik! It looks like il be going with the 4.10's my truck runs great going down the track just need more to get goin out of the hole to get that 60 ft down...Thanks guys for the help!
Next time i go to the track il have to let you know about the results!

I have an almost brand new auburn posi for the 12 bolt truck rear if your interested